Embodiments of the present invention are directed to methods and apparatus for interbody distraction and implant/transplant insertion.
Intervertebral devices (commonly known as interbody spacers, and allograft transplants) have been developed for use in the reconstruction of collapsed inter-vertebral and/or otherwise damaged disc spaces. Herein, a gap separating two adjacent bodies may be referred to as an interbody cavity. A gap separating two adjacent vertebral bodies may be referred to as an intervertebral cavity or space.
In some procedures, surgeons insert these intervertebral devices into the intervertebral space of a patient's spine to facilitate bone fusion between and into the contiguous involved vertebrae. This fusion creates a new solid bone mass, which acts to hold the spinal segment at an appropriate biomechanically restored height as well as to stop motion in a painful segment of the spine. Intervertebral devices surgically placed in such involved interbody regions can thus stimulate interbody bone in-growth such that the operated anterior spinal segments heal into a contiguous bone mass, i.e., fusion occurs.
Additionally and/or alternatively, surgeons use intervertebral devices (and/or biological alternatives) to provide weight bearing support between adjacent vertebral bodies, and thereby correct or alleviate a variety of clinical problems. In this regard, surgeons use intervertebral devices for surgical therapy for degenerative disc disease (DDD), discogenic low back pain, spondylolisthesis, and/or reconstruction following tumor or infection surgery, and other spine related maladies requiring surgical intervention.
In many implant designs, a relatively hard or sturdy implant construct is formed from a selected biocompatible material such as metal, ceramic, or carbon fiber-reinforced polymer. This implant construct often has a partially open or porous configuration and is coated or partially filled with a selected bone ingrowth-enhancing substance, such as harvested bone graft supplied from the patient, human donor allograft bone transplant material supplied by a tissue bank, genetically cultivated bone growing protein substitutes, and/or other biological/biochemical bone extenders. Such devices, when implanted into the intervertebral space, promote ingrowth of blood supply and grow active and live bone from the adjacent spinal vertebrae to inter-knit with the implant, thereby eventually immobilizing or fusing the adjacent spinal vertebrae. Such implants also commonly include a patterned exterior surface such as a ribbed or serrated surface, or screw thread geometry, to achieve enhanced mechanical locking with the adjacent vertebrae during the bone ingrowth/fusion process.
The inventory of available intervertebral devices has expanded to include machined, transplantable allograft bone spacers. Bone Banks and tissue processors are able to precision-engineer donated human bone to specific vertebral interbody milled dimensions most likely to fit into the affected intra-discal zones. For many surgeons, these biological devices may provide a better option for a particular patient than the use of man-made materials.
The intervertebral or interbody implants of these general types have achieved a significant degree of clinical success. Notwithstanding this success, a variety of problems arise in connection with surgical interbody implant placement. Surgeons can have difficulty with the implantation process because of individual pathology, deformity, anatomical space restraints, or implant material limitations. Often, implant placement proves a difficult and time-consuming procedure when the soft tissue of the support elements of the adjacent vertebrae degenerate, causing collapse of the spaces between the vertebrae. This degenerative condition, coupled with compromised adjacent tissues, nerves and vasculature, may impede physical and visual access to the intervertebral space.
Spine surgery of this type may require removal of the remaining disc material, release of the contracted soft tissues around the intervertebral disc space, and some degree of distraction or pulling apart of the adjacent vertebrae in an attempt to restore disc space height, realign the spine, and indirectly decompress the nerve roots exiting the spine posteriorly at the affected level. This distraction procedure has traditionally required the use of several surgical distraction instruments, which may increase the overall complexity of the procedure, intensify the invasiveness of the surgical procedure, and possibly lead to iatrogenic vascular and neurosurgical injuries which can cause intraoperative surgical complications. At the same time, use of multiple instruments may limit the surgeon's manual access and clear view of the involved intervertebral space.
After the surgeon removes the disc material, a clean aperture should remain in which to place the intervertebral implant device. Typically, the surgeon grasps the device with a special pliers-like tool and places it at the mouth of the aperture. Then the surgeon typically uses extreme force as he or she hammers on the tool so that the implant device achieves its final placement. This hammering technique applies enormous shear forces through the implant device. As the implants have material and engineering limitations, such forces may cause the implant to fracture, shear, or break apart as a result of the forceful insertion. In addition, some implant designs require materials which do not tolerate the use of impaction-type forces that are so often necessary to advance the implant into the intervertebral space.
A variety of intervertebral implant insertion instruments have been developed in recent years as a result of efforts to simplify surgical distraction of the intervertebral space, while facilitating placement of the implant therein. See, for example, U.S. Pat. Nos. 6,755,841; 6,478,800; and 6,652,533; and U.S. Publication No. 2005/0165408 which disclose instruments for advancing an intervertebral implant between a pair of pivotally mounted distraction levers used to engage and distract adjacent vertebral structures. In these designs, the advancing movement of the implant is accompanied by wedged separation of the distal end tips of the levers which are engaged with and thereby separate or distract the adjacent vertebral structures.
While such implant insertion instruments provide a significant improvement in the art, the implant is not always safeguarded against substantial and potentially undesirable compression and shear forces during such advancing displacement between the pivoting distraction levers. In addition, these instruments have not provided a simple mechanism for quickly and easily retracting the distal end tips of the levers from the distraction space following intervertebral placement of the implant. Moreover, these instruments have not provided the ability to accommodate implants of different sizes, such as implants having different height dimensions, which may be indicated by specific patient requirements, without altering the insertion angle of the distal end tips of the distraction levers. In this regard, an amplified increase in the tip insertion angle, associated with implantation of a significantly taller implant, can undesirably increase the complexity and difficulty of the surgical implantation procedure.
Further advancements in insertion instruments and procedures are disclosed in co-pending U.S. patent application Ser. No. 11/622,545, filed Jan. 12, 2007, the entire disclosure of which is hereby incorporated by reference. The instruments and procedures disclosed therein provide for insertion of an implant without requiring the hammering technique and resultant shear forces through the implant device. Instead, respective ramps (at a given angle with respect to one another) are inserted into the intervertebral disc space and vertebral distraction is carried out by separating the ramps while keeping the angle fixed. Once the vertebrae are distracted, the implant slides along the ramps into position without any loading and/or insertion forces. When the implant is in place, the ramps are moved towards one another (again maintaining the given angle), which gently applies the vertebral loading to the implant and permits removal of the ramps from the intervertebral space.
Although the insertion instruments and procedures of U.S. patent application Ser. No. 11/622,545 represent a significant advancement over the art, there is still room for improvement. There exists, therefore, a continuing need for improvements in and to intervertebral implant insertion instruments and related intervertebral implants for use therewith, particularly with respect to quickly and easily distracting the intervertebral space for facilitated placement of an implant having a range of different heights, for safeguarding the implant against compression and shear forces during intervertebral distraction and insertion.